1. Field of the Invention
This invention relates broadly to the field of event sequencers and in particular, relates to an electronic sequencing system that combines the outputs of a plurality of identically operating redundant sequencers to provide a highly reliable sequencing system for demanding applications such as in space vehicles.
2. Brief Description of the Prior Art
Sequencers are used, for example, to control the timing and sequence of events in connection with the launching or in-flight maneuvering of spacecraft. Such sequencers for applications in spacecraft traditionally have been mechanical, utilizing motor driven gears and cams in order to provide the necessary high degree of reliability. See U.S. Pat. No. 4,018,092, issued to Fletcher, for a "Mechanical Sequencer." Although reliable, such sequencers have important disadvantages when used in spacecraft. First, mechanical sequencers have a limited timing accuracy. Second, such sequencers are often heavy and bulky and thus reduce the amount of other productive equipment that can be carried by a spacecraft. Third, such sequencers are inflexible. A change in the sequence requires tedious and time-consuming modifications of gears and cams.
Accordingly, it is an object of the invention to provide a sequencer that has the capability to time events in time increments of minimal size.
It is also an object of the invention to provide a sequencer which possesses a high degree of reliability for applications such as use in space.
It is a further object of the present invention to provide a flexible apparatus for sequencing so that a change in the sequence can be accomplished easily on the ground or in space by electrical commands without modifying mechanical components.
It is another object of this invention to provide an apparatus that is easy to maintain and repair.
It is a further object of the invention to provide a sequencer that has weight, volume and safety characteristics that permit its use in space.